mysql - Mysql子查询选择

Question

我试图找到一个解决方案：

我需要选择所有任务的查询，这些任务不是started和此任务的类似任务名称不应该在此表中重复 5 行并带有标志started

我的查询：

SELECT * FROM tasks as t 
WHERE started = 0 
AND ((SELECT COUNT(*) FROM tasks 
WHERE started = 1 AND taskname = taskname) < 5)

但查询不起作用。谁能告诉我我做错了什么？

Answer 1

尝试以下

AND taskname = t.taskname

Answer 2

你非常接近：

SELECT * FROM tasks as t 
WHERE started = 0 
AND (SELECT COUNT(*) FROM tasks 
WHERE started = 1 
AND taskname = t.taskname) < 5

您只需要比较计数结果而不是在子查询中包含比较。t.此外，您需要使用前缀将任务名限定为外部表